Ultrasonic biometric sensor
An ultrasonic biometric sensor comprises a detection chip. The detection chip includes a substrate, an ultrasonic transducer array and a control circuit. The ultrasonic transducer array is arranged on the substrate, including a plurality of arrayed piezoelectric elements. Each piezoelectric element is disposed on a floating membrane. The floating membrane is suspended in the opening side of a cavity by at least one support arm extending transversely. The control circuit is also arranged on the substrate and electrically connected with each piezoelectric element through the support arm to control the ultrasonic transducer array to generate an ultrasonic signal and read the reflected ultrasonic signal received by the ultrasonic transducer array. The ultrasonic biometric sensor is easy to fabricate and has a high yield.
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The present invention relates to a biometric sensor, particularly to an ultrasonic biometric sensor.
2. Description of the Prior ArtThe capacitive fingerprint sensor is a widely-used biometric sensor at present. However, the capacitive fingerprint sensor has poorer penetration capability, hard to penetrate the glass panel of a mobile Internet device (such as a mobile phone). Further, a wet or sweating finger is likely to affect the contrast of the image captured by the capacitive fingerprint sensor. Besides, the oil stain of a fingerprint may be cast into a dummy fingerprint. In other words, the capacitive fingerprint sensor is inferior in counterfeit-proof and vulnerable in security.
Ultrasonic waves can penetrate common case material of mobile phones, such as glass, aluminum, stainless steel, quartz and plastic, to scan fingerprints. Furthermore, ultrasonic waves can penetrate the surface of skin to detect 3D details and characteristics of fingerprints, such as friction ridges and sweat pores. Compared with the capacitive fingerprint sensor, the ultrasonic fingerprint sensor is superior in penetrability, 3D imaging capability, and anti-counterfeit capability. Therefore, the ultrasonic finger print sensor is an alternative high-performance biometric sensor for the applications of personal identification.
The ultrasonic fingerprint sensor is based on the acoustic impediography. While propagating in media of different densities and encountering different acoustic impedances, ultrasonic waves will generate different reflection waves intensity. Refer to
Γ=(Zi−Z0)/(Zi+Z0)
Wherein Zi is the acoustic impedance of the ridge R or valley V. When Γ is a negative value, it indicates that the phase of reflected wave is 180 degrees. In
Refer to
Therefore, there is a need to manufacture ultrasonic fingerprint sensor without using the wafer bonding technology.
SUMMARY OF THE INVENTIONThe present invention provides an ultrasonic biometric sensor, wherein a control circuit and an ultrasonic transducer array are fabricated on an identical substrate, whereafter an anisotropic etching process is used to form a cavity below each piezoelectric element of the ultrasonic transducer array, wherefore the present invention can fabricate an ultrasonic biometric sensor without using the wafer bonding technology, whereby the present invention can increase the yield and productivity and lower the fabrication cost.
In one embodiment, the ultrasonic biometric sensor of the present invention comprises a detection chip. The detection chip includes a substrate, an ultrasonic transducer array and a control circuit. The substrate has a first region and a second region. The ultrasonic transducer array is arranged on the first region and includes a plurality of arrayed piezoelectric elements. Each piezoelectric element is disposed in a floating membrane. The floating membrane is suspended in the opening side of a cavity by at least one support arm extending transversely. The control circuit is arranged on the second region and electrically connected with the piezoelectric elements through the support arms. The control circuit controls the ultrasonic transducer array to generate an ultrasonic wave and reads the reflected ultrasonic signal received by the ultrasonic transducer array.
Below, embodiments are described in detail in cooperation with the attached drawings to make easily understood the objectives, technical contents, characteristics and accomplishments of the present invention.
The present invention will be described in detail with embodiments and attached drawings below. However, these embodiments are only to exemplify the present invention but not to limit the scope of the present invention. In addition to the embodiments described in the specification, the present invention also applies to other embodiments. Further, any modification, variation, or substitution, which can be easily made by the persons skilled in that art according to the embodiment of the present invention, is to be also included within the scope of the present invention, which is based on the claims stated below. Although many special details are provided herein to make the readers more fully understand the present invention, the present invention can still be practiced under a condition that these special details are partially or completely omitted. Besides, the elements or steps, which are well known by the persons skilled in the art, are not described herein lest the present invention be limited unnecessarily. Similar or identical elements are denoted with similar or identical symbols in the drawings. It should be noted: the drawings are only to depict the present invention schematically but not to show the real dimensions or quantities of the present invention. Besides, matterless details are not necessarily depicted in the drawings to achieve conciseness of the drawings.
Refer to
The control circuit 23 is arranged on the second region 212. The control circuit 23 is electrically connected with each piezoelectric element 221 through the support arms 223. The control circuit 23 controls the ultrasonic transducer array 22 to generate ultrasonic waves and reads the reflected ultrasonic signals received by the ultrasonic transducer array 22. In the embodiment shown in
Refer to
In one embodiment, the ultrasonic biometric sensor of the present invention further comprises a packaging substrate 30 and a passive element 31. The packaging substrate 30 includes a plurality of electric-conduction contacts 32 for external electric connection. In one embodiment, the packaging substrate 30 is made of polyimide (PI). The passive element 31 is arranged on a first surface of the packaging substrate 30. The detection chip 20 is also arranged on the first surface of the packaging substrate 30. In other words, the passive element 31 and the detection chip 20 are disposed on the same side. The detection chip 20 is electrically connected with the electric-conduction contacts 32 and the passive element 31 through the external electric-conduction contacts 214 of the substrate 21 and the electric-conduction traces on the packaging substrate 30. In one embodiment, the electric-conduction contacts 214 have a plurality of metal bumps 25 that can be joined with the packaging substrate 30 in a eutectic bonding technology, whereby the detection chip 20 and the packaging substrate 30 are assembled together and connected electrically. In one embodiment, the detection chip 20 is fixed to the packaging substrate 30 through a plurality metal bumps 25 and an anisotropic conductive film (ACF).
In one embodiment, the ultrasonic biometric sensor of the present invention further comprises a filling material 26 that is filled into the gaps between the detection chip 20 and the packaging substrate 30 to eliminate the gaps containing air. In one embodiment, the filling material 26 is a silica gel. After package, an adhesive glue 41 is used to fix the ultrasonic biometric sensor to a plate 40 that the user can touch, such as a faceplate or casing of a smart phone. While the finger of the user touches an area of the plate 40, which is within the sensing area of the ultrasonic transducer array 22, the ultrasonic biometric sensor of the present invention can read the fingerprint or another biometric characteristic of the user to verify the identity of the user.
Below is described the method for fabricating the ultrasonic biometric sensor of the present invention. Refer to
Refer to
In one embodiment, aluminum nitride (AlN), which will not generate pollution in the CMOS process, is used as the piezoelectric material. A reactive pulse-DC magnetron sputtering process is used to form an AlN layer. Next, a dry etching process or a wet etching process using tetramethylammonium hydroxide (TMAH) as the etching liquid is used to remove a portion of AlN and define the pattern of the piezoelectric element 221.
In one embodiment, lead zirconate titanate (PZT) is used as the piezoelectric material. A sputtering method, which is disclosed in a US patent application No. US 2014/0049136 A1, is used to form a PZT thin film. Next, a dry etching method or a wet etching method is used to remove a portion of PZT and define the pattern of the piezoelectric element 221.
Refer to
Then, open the etched windows, and use an anisotropic etching method and a tetramethylammonium hydroxide (TMAH) solution as the etching agent to remove a portion of the substrate 21, which is below the piezoelectric elements 221, to form the cavities 213 and the floating membranes 222 suspending in the opening end of the cavities 213, as shown in
It should be explained: the ultrasonic transducer array and the control circuit are transversely arranged on the substrate in the abovementioned embodiments. However, the present invention is not limited by the abovementioned embodiments. In other embodiments, a multilayer structure and a sacrifice layer can be used to arrange the ultrasonic transducer array and the control circuit in a vertical way.
In conclusion, the present invention proposes an ultrasonic biometric sensor, wherein the control circuit and the ultrasonic transducer array are fabricated on an identical substrate, whereafter in an MEMS (microelectromechanical system) process, an anisotropic etching process is used to form a cavity below each piezoelectric element of the ultrasonic transducer array, wherefore the ultrasonic biometric sensor of the present invention can be fabricated without using the wafer bonding process, whereby the yield and productivity is increased and the fabrication cost is decreased.
Claims
1. An ultrasonic biometric sensor comprising:
- a detection chip including: a substrate having a first region and a second region; an ultrasonic transducer array arranged on the first region and including a plurality of arrayed piezoelectric elements, wherein each piezoelectric element is disposed on a floating membrane, and wherein the floating membrane is suspended in an opening side of a cavity by at least one support arm extending transversely; and a control circuit arranged on the second region and electrically connected with each piezoelectric element through the support arm to control the ultrasonic transducer array to generate an ultrasonic wave and read a reflected ultrasonic signal received by the ultrasonic transducer array.
2. The ultrasonic biometric sensor according to claim 1, wherein a projection of the cavity to the substrate is larger than or equal to a projection of the floating membrane to the substrate.
3. The ultrasonic biometric sensor according to claim 1, wherein the cavity is formed in an anisotropic etching method.
4. The ultrasonic biometric sensor according to claim 1, wherein a side wall of the cavity is an inclined surface.
5. The ultrasonic biometric sensor according to claim 1, wherein a material of the piezoelectric element comprises polyvinylidene difluoride (PVDF), a mixture of polyvinylidene difluoride (PVDF) and trifluoroethylene (TrFE) (PVDF-TrFE), aluminum nitride (AlN) or lead zirconate titanate (PZT).
6. The ultrasonic biometric sensor according to claim 1, wherein the control circuit includes:
- a controller generating a clock signal to control the ultrasonic transducer array to generate the ultrasonic wave;
- a signal processor electrically connected with the controller and the ultrasonic transducer array to process the reflected ultrasonic signal received by the ultrasonic transducer array to enable the controller to output a biometric verification signal; and
- a communication interface electrically connected with the controller and enabling the ultrasonic biometric sensor to communicate with an external device.
7. The ultrasonic biometric sensor according to claim 6, wherein the communication interface comprises a serial peripheral interface (SPI) or a universal serial bus (USB).
8. The ultrasonic biometric sensor according to claim 1 further comprising:
- a protection layer covering the ultrasonic transducer array and the control circuit.
9. The ultrasonic biometric sensor according to claim 8, wherein a material of the protection layer comprises a photoresist material or polyimide.
10. The ultrasonic biometric sensor according to claim 1 further comprising:
- a packaging substrate having a plurality of electric-conduction contacts; and
- at least one passive element arranged on a first surface of the packaging substrate, wherein the detection chip is arranged on the first surface of the packaging substrate and electrically connected with the plurality of electric-conduction contacts and the at least one passive element.
11. The ultrasonic biometric sensor according to claim 10, wherein a material of the packaging substrate includes polyimide.
12. The ultrasonic biometric sensor according to claim 10, wherein the detection chip is joined with the packaging substrate through a plurality of metal bumps in a eutectic bonding method.
13. The ultrasonic biometric sensor according to claim 10, wherein the detection chip is fixed to the packaging substrate through an anisotropic conductive film.
14. The ultrasonic biometric sensor according to claim 10 further comprising:
- a filling material filled into gaps between the detection chip and the packaging substrate.
15. The ultrasonic biometric sensor according to claim 1, wherein the piezoelectric element has a working frequency within 20-30 MHz.
20150165479 | June 18, 2015 | Lasiter |
20180129849 | May 10, 2018 | Strohmann |
20180369866 | December 27, 2018 | Sammoura |
Type: Grant
Filed: Jan 8, 2018
Date of Patent: May 28, 2019
Patent Publication Number: 20180211081
Assignee: ORIENTAL SYSTEM TECHNOLOGY INC. (Hsinchu)
Inventors: Chein-Hsun Wang (Hsin-Chu), Wen-Chie Huang (Hualien County)
Primary Examiner: Tom Y Lu
Application Number: 15/864,326
International Classification: G06K 9/00 (20060101); G06F 21/32 (20130101);